\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\begin{document}
\small
\begin{tikzpicture}[>=stealth,scale=1.6]
  \useasboundingbox(-2.65,-1.95)rectangle(0.65,1.35);
  \draw [->,very thick](0,0)--(180:2)node [above]{$v_A$};
  \draw [->,very thick](0,0)--(180+30:2)node [below]{$v_B$};
  \draw [->,very thick](180:2)--node [left]{$\Delta v$}(180+30:2);
  \draw (0-1,0) arc (180:180+30:1) node [midway,left]{$\Delta \phi$};
\end{tikzpicture}
\end{document}